Turbine bucket blades



Nov. 1, 1960 R. e. FRANK TURBINE BUCKET BLADES 2 Sheets-Sheet 1 FiledNov. 20, 1958 M L WM m 'l l' il INVENTOR. X085? 6'. F/FM'A W4. A? MawNOV. 1, 1960 R, G, FRANK 2,958,505

TURBINE BUCKET BLADES Filed Nov. 20, 1958 2 Sheets-Sheet 2 46 JNVENTOR.

fii 2,958,505

Patented Nov. 1, 1960 TURBINE BUCKET BLADES Robert G. Frank, Cincinnati,Ohio, assignor to the United v Filed Nov. 20, 1958, Ser. No. 775,330

2 Claims. (Cl. 253-39.15)

The present invention relates generally to turbine blades or buckets foruse under high temperature conditions, and as illustrated herein,relates more particularly to turbine blades or buckets having coolingpassages therein.

The high temperatures incident to the combustion of jet and rocket fuelshas made it necessary to form turbine blades from metals or othermaterials which are substantially free from oxidation. However, newdesigns in reaction motors have resulted in highly increased inlettemperatures which are destructive of previously known turbine blades.Under earlier conditions the use of molybdenum and molybdenum alloysgave satisfactory results and destruction of the surfaces of the turbineblade due to high temperature oxidation was not a problem. However, gastemperatures may now range from about 2000 F. to about 2600 F. and solidmolybdenum, molybdenum alloys and ceramic coated molybednum andmolybdenum alloys corrode to such an extent that virtual destruction ofthe turbine blades may result.

It has been discovered, however, that hollow air cooled bladesfabricated from conventional materials may be used in aircraft jetturbines. The strength of these blades or buckets is limited because ofthe inherent low strength of the materials of which the buckets areformed. It was found, however, that if the blades were fabricated frommolybdenum wire clad or plated with a material highly resistant tooxidation would have sufficient strength, be of light weight and couldbe readily fabricated while still protecting the blades from oxidationat temperatures ranging from about 2000 F. to about 2600 F.

One object of the present invention, accordingly, is to provide turbineblades which are oxidation resistant at relatively high combustiontemperatures. To this end and as illustrated, the invention contemplatesthe use of molybdenum wire clad or plated with an oxidation resistantmaterial and encased in a sheath of oxidation resistant material.

With the above and other objects in view the invention will now bedescribed with particular reference to the accompanying drawings inwhich:

Fig. 1 is a view in elevation of one form of turbine bucket embodyingthe present invention;

Fig. 2 is a view in section taken along the lines II-II of Fig. 1;

Fig. 3 is a view in section similar to that shown in Fig. 2 butillustrating another embodiment of the invention;

Fig. 4 illustrates another embodiment of the invention but before theparts of the sheet are secured together at their leading and trailingedges;

Fig. 5 illustrates another form of the invention with the sheath in thefiat; and

Fig. 6 is a view of the construction shown in Fig. 5 before the leadingedges of the turbine bucket are welded together.

The purpose of the present invention is to provide aircooled turbinebuckets which are able to withstand the high temperatures and highstrains incident to the use of modern fuels in turbojet engines.Molybdenum wire or wires fabricated from tungsten, columbium, or nickelbase alloys could be used so long as the intended operating temperatureremains below the recrystallization temperature' of the material.

The present invention contemplates the use of high strength-hightemperature wire as a supporting frame having suificient strength towithstand the high strains to which the buckets are subjected duringuse. Preferably molybdenum wire is used but any of the wire materialsreferred to just above will be satisfactory.

The construction shown in Fig. 1 comprises a root portion It) and abucket or airfoil section 12. The root portion 10 is of usual shape andconstruction and need not be described in further detail herein. Theairfoil section 12 is seated in a suitable shaped recess 14 in the rootportion 10 and in which the completed airfoil is suitably brazed orwelded. The airfoil section 12, as illustrated in Fig. 2, is composed ofa plurality of rods or wires 16 of varying size which are coated with asuitable brazing alloy. The coated wires 16 are arranged parallel andcontiguous to each other along the lateral center line of the blade andare assembled within a suitable sheath 18 formed preferably of chromiumplate.

The shield 18 and the wires 16 assembled therewith are placed in anautoclave to fuse the brazing alloy to secure the wires 16 to each otherand to the sheath 18 as shown at 20 and 22, respectively, in Fig. 2. Itis to be noted that only sufiicient brazing alloy is used to permit theparts to be secured together without entirely filling the space be tweenadjacent wires 16 and the sheath 18. Thus, a plurality of spaces 24 areprovided which extend the entire length of the turbine buckets 12 andthrough which cooling air may be forced. It was previously stated thatthe root portion 10 was provided with a suitable shaped recess 14- inwhich the base portion of the airfoil section 12 is secured either bybrazing or welding. There is provided an air duct 26 through whichcooling air may be drawn and passed through the cooling passages 24.

The invention, however, is not limited to the modification shown in Fig.2 since the central portion of the bucket 12 may be hollow and providedwith an internal lining formed of wires 28 which are substantiallyuniform in diameter and are so closely spaced that they aresubstantially in contact with each other. The wires 28 are coated with asuitable brazing or welding alloy. The wires 28 are assembled andsupported in a suitable jig or fixture to form an airfoil section suchas shown in Fig. 3. The shaped wire section has placed thereover asuitable sheath 30' which fits closely against the wires 28. Theassembled wires 28 and sheath '30, together with jig with which they aresupported are placed in an autoclave to permit the brazing or weldingalloy to be fused to secure the wires 28 to each other and to the innersurface of the chromium coated sheath 30. After the brazing or weldingoperation has been completed the assembly is removed from the jig andsurplus lengths of wire are trimmed at the top and bottom end portionsof the sheath 30.

The bucket 12, as constructed above, is then placed in a recess 14 andsuitably secured in place by brazing or welding. The bucket 12 shown inFig. 3 has a hollow interior portion 32 which communicates with the airduct 26 through which suitable air or other fluid may be passed tomaintain the temperature of the bucket 12 substantially below the hightemperature of the inlet gases of the axial flow turbine.

There are shown in Figs. 4, 5 and 6 two other forms of the invention,which, however, when assembled display a cross-sectional area similar tothe one shown in Fig. 3. In the modification shown in Fig. 4, a sheath34 is shaped to form a root section 36 and a bucket section 38. Thebucket or airfoil section 38 is coated with a suitable braz- 3 ing orwelding alloy and high strength molybdenum or other high temperaturealloy wires are suitably brazed or secured to the inner surface of atleast one side of the sheath 38. Preferably, both sides of the sheath 38are provided with e1ose1yspaced1wires 40 which are arranged in anairfoil section substantially similar to that shown in Fig. 3. It is tobe noted that the airfoil section itself is of substantial thickness atthe root section 36 and tapers from the root section toward the outerend of the blade or airfoil section 38. After the wire 40 has beensecured in position the assembled bucket is placed in a suitable jig orfixture and maintained in shaped position to permit the leading andfollowing edges of the airfoil section to be secured together bysuitable brazing or weld- As illustrated, the construction shown in Fig.4 has a root section which differs from that shown in Fig. l, but it isapparent that the hub of the turbine wheel may be suitably shaped toreceive the substantially cylindrical root portion shown in Fig. 4. v VThe construction shown in Fig. 5 is somewhat similar to the constructionshown in Fig. 4, except that the portions of the sheath 42 are formed inone section and in side by side relation so that the right hand portionof the sheath 42 may be folded over the left hand portion of the sheath42 and suitably shaped to form an airfoil turbine bucket section.

The modification shown in Fig. 5 is provided with a series of wires 44which are coated with suitable alloy and secured to the sheath 42 in thesame manner that the wires 40 are secured to the sheath 38, except thatthe wires extend from the top to the bottom of the sheath and thusextend into the root section 46 as shown in Figs. 5 and 6. Here again,it maybe necessary only to provide one side of the. sheath with wires.However, preferably both sides of the sheath are provided with wires sothat the airfoil section is similar to the construction shown in Fig. 3,rather than to the construction shown in Fig. 2, which would be the casewhen only one side of the sheath 42 was provided with wires. After thesheath 42 has been provided with properly positioned wires it is foldedalong the line 48 which may form either the leading or followingedgeofthe bucket blade and is then placed in a suitable jig or die to bringthe other longitudinal edges of the bucket close together to permit themto be secured by suitable brazing or welding to form a turbine buckethaving the airfoil contours as shown in Fig. 3. At the same time theroot section 46 is curved inwardly at the lower end to form a rootportion for securing the bucket to a suitable hub.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent of the United States is:

..1. A fabricated blade for an axial flow rotor comprising a hollowmetal sheath of airfoil cross section, a series of round metal rodswithin said sheath arranged contiguously with their centers along thechord of said airfoil, said rods being of diameters td'siibstanuan fillsaid sheath, and means to secure 'said'rods to .each other and to saidsheath at their points of contact thereby allowing 'voids at theinterstices between adjacent rods and said sheath.

2. n A fabricated blade of airfoil cross section comprising a hollowmetallic sheath of said airfoil cross section, a reinforcingsection;s'aid reinforcing section comprising a series of'contighous, round metalrods arranged within said sheath with their centers along the chord ofsaid airfoil cross section, the end rods in said sheath being inintimate contact with said sheath and one adjacent rod, the remainder ofsaid rods being in intimate contact with adjacent rods and with oppositesurfaces of said hollow metallic sheath, and means for securing saidrods and said sheath together to allow voids at the interstices betweenthe rods and said sheath.

References Cited in the file of this patent UNITED STATES PATENTS

